if the half time of a substance A is 0.5 years how long would it take for 2 grams of substance A to remain given an initial mass of 16 grams

The following reaction shows the products when sulfuric acid and aluminum hydroxide react. al(oh)3 + h2so4 → al2(so4)3 + h2o the table shows the calculated amounts of reactants and products when the reaction was conducted in a laboratory. initial mass and yield sulfuric acid aluminum hydroxide initial amount of reactant 40 g 15 g theoretical yield of water from reactant 14.69 g 10.38 g what is the approximate amount of the leftover reactant? 11.73 g of sulfuric acid 10.33 g of sulfuric acid 11.12 g of aluminum hydroxide 13.67 g of aluminum hydroxide

Embryos of different species look very similar, which shows that the organisms share a ancestor.

Can someone me with questions 12 and 13 plz.